PORT_CLK_SEL programming is needed only on HSW/BDW.

v2:
- don't program PORT_CLK_SEL from mst encoders either (imre)
v3:
- fix the check for GEN9+ in intel_mst_pre_enable_dp() (damien)
Signed-off-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NSagar Kamble <sagar.a.kamble@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>